The total and T-lymphocyte counts, different types of lymphocytic surface immunoglobulins and levels of serum immunoglobulins were studied in 112 consecutive patients with chronic lymphocytic leukemia in order to investigate possible correlations between the immunological picture and the different stages according to the staging criteria recently proposed by Binet et al. Patients were also subdivided according to the form of their disease, "indolent" or "active", and correlations with the immunological picture investigated. The total lymphocyte count showed a significantly increasing trend through the three different stage (p less than 0.01), and it was higher in the "active" than in the "indolent" disease (p less than 0.01). Also the number of T-lymphocytes increased in the "active" forms (p less than 0.01). No statistically significant correlations were observed between the different surface immunoglobulin subclasses and the clinical pattern. As regard the various classes of serum immunoglobulins, the number of patients, with a reduction of at least one of the classes tended to increase with worsening of the clinical stage.